Mortality among maintenance employees potentially exposed to asbestos in a refinery and petrochemical plant

Our plain-English summary of Mortality among maintenance employees potentially exposed to asbestos in a refinery and petrochemical plant, by S.P. Tsai, L.C. Waddell, E.L. Gilstrap, et al (American Journal of Industrial Medicine, 1996).

The study

• Authors: S.P. Tsai, L.C. Waddell, E.L. Gilstrap, J.D. Ransdell, C.E. Ross
• Journal: American Journal of Industrial Medicine
• Published: 1996;29(1):89-98
• Cited by: 54 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This paper reports the mortality experience from 1948 to 1989 of 2,504 maintenance employees who had a minimum of one year of employment in jobs with potential exposure to asbestos at a Texas refinery and petrochemical plant. For the purposes of this study, "potential exposure" is equated with those jobs or crafts having the greatest direct potential proximity to, or which worked directly with, asbestos-containing materials, especially asbestos-containing thermal insulation. Approximately one-half of the study population had 10 years or longer potential exposure, and 80% had their first potential exposure before 1970. The total population exhibited significantly lower mortality for all causes, the standardized mortality ratio (SMR = 77); and for all cancer (SMR = 85), as compared to residents in the surrounding communities. Statistically significant deficits in mortality were also observed in a number of noncancerous diseases such as heart disease (SMR = 78; 95% CI = 69-88), nonmalignant respiratory disease (SMR = 70; 95% CI = 50-95), and cirrhosis of the liver (SMR = 44; 95% CI = 22-79). Mortality among employees who had 20 years or longer since their first potential exposure was also examined; the pattern of mortality was similar to that exhibited by the total cohort, with a slight increase in the SMR for most of the causes. The only statistically significant excess of mortality found was a fourfold increase in mesothelioma (5 observed and 1.2 expected deaths) the SMR was 428 (95% CI = 139-996) for the total cohort and was 469 (95% CI = 152-1093) for those who had 20 years or more since first potential exposure. In contrast to asbestos industry worker studies, mortality for lung cancer was substantially lower than the general population (SMR = 81; 95% CI = 63-103). The observed number of deaths for cancer of the larynx was virtually the same as expected (3 observed vs. 2.8 expected). This study also showed decreased mortality for cancers of gastrointestinal organs such as the esophagus (SMR = 78), stomach (SMR = 63), large intestine (SMR = 91), rectum (SMR = 55), or pancreas (SMR = 90)--cancers that have been reported to be elevated in studies of various industry workers directly exposed to asbestos.

In plain English

This study followed deaths from 1948 to 1989 among 2,504 men at Shell's Deer Park refinery and petrochemical complex in Texas. All had worked at least one year in jobs with the greatest potential asbestos exposure, mostly maintenance crafts. Expected deaths came from Harris County, Texas rates. For mesothelioma, the expected number was estimated from SEER cancer incidence rates, assuming pre-1970 rates were half the 1973-1980 rates or lower. Deaths from all causes (SMR 77) and all cancers (SMR 85) were significantly below expected. Of more than 60 causes examined, only mesothelioma was significantly raised. There were 5 mesothelioma deaths versus 1.2 expected (SMR 428; 95% CI 139-996). The SMR was 469 (95% CI 152-1,093) among 1,821 workers followed from 20 years after first assignment to a potentially exposed job. Lung cancer deaths were lower than expected (SMR 81; 95% CI 63-103). Laryngeal cancer deaths matched expectation, and no individual digestive cancer was increased. The authors concluded that asbestos exposure in maintenance work here was sufficient to produce excess mesothelioma but not lung cancer. Pre-1970s exposure monitoring data were limited, so exposures were not precisely quantified.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective cohort mortality study. Observed deaths were compared with expected deaths calculated from Harris County, Texas rates (standardized mortality ratios, SMRs). For mesothelioma, the expected number was estimated from SEER incidence rates. This assumed that rates before 1970 were one-half the 1973-1980 rates or lower.
• Who was studied: 2,504 male employees of Shell's Deer Park Manufacturing Complex (DPMC), a refinery and petrochemical plant in Texas. Each had at least 1 year in the designated jobs. They were followed from 1948 to December 31, 1989, contributing 68,632 person-years. Nonwhite employees made up 17% of the cohort.
• Exposure: At least one year in jobs with the greatest potential asbestos exposure: insulator, pipefitter, boilermaker, electrician, welder, carpenter and laborer. The main source was removal, repair or reapplication of asbestos-containing thermal insulation, which was used until the early 1970s. A Shell industrial hygienist's review found chrysotile was the predominant fiber in insulation samples; amosite and crocidolite were sometimes found. Exposure monitoring data from before the 1970s were limited, and exposures were not quantified.
• Main results:
  • Whole cohort: deaths from all causes were significantly lower than expected (SMR 77; 95% CI 72-83).
  • Whole cohort: deaths from all cancers were significantly lower than expected (SMR 85; 95% CI 73-98).
  • Whole cohort: of more than 60 causes of death examined, only mesothelioma showed a statistically significant increase.
  • Whole cohort: 5 deaths had mesothelioma mentioned on the death certificate. The expected number was estimated as 1.2 from SEER incidence rates, with an assumption about pre-1970 rates. This gave an SMR of 428 (95% CI 139-996).
  • Workers with 20 or more years of potential exposure: the SMR for mesothelioma was 645 (95% CI 78-2,329), based on 2 deaths. The upward trend in mesothelioma SMRs with longer exposure was not statistically significant.
  • Subgroup of 1,821 employees, followed from 20 years after their first assignment to a potentially exposed job: the SMR for mesothelioma was 469 (95% CI 152-1,093), which was statistically significant.
  • Whole cohort: lung cancer deaths were lower than in the general population (68 observed, 84.0 expected; SMR 81; 95% CI 63-103).
  • Whole cohort: laryngeal cancer deaths were about as expected (3 observed vs 2.8 expected).
  • Whole cohort: SMRs were below 100 for cancers of the esophagus (63; 95% CI 17-160), stomach (69; 95% CI 25-149), colon and rectum combined (85; 95% CI 50-136) and pancreas (72; 95% CI 31-143). No individual digestive cancer site showed increased mortality.
  • Whole cohort: deaths from nonmalignant respiratory disease were significantly lower than expected (SMR 70; 95% CI 50-95). Only one death certificate indicated asbestosis.
  • Whole cohort: lymphosarcoma and reticulosarcoma deaths were raised, but not statistically significantly (5 observed, 3 expected; SMR 166; 95% CI 54-387).
• The authors' conclusion: The authors concluded that the asbestos exposure characteristic of maintenance work at this facility was sufficient to produce excess mesothelioma but not sufficient to produce lung cancer.
• Limitations the authors state:
  • A lack of quantitative exposure data meant a more precise exposure-effect analysis was not possible.
  • Exposure monitoring data from before the 1970s were limited, and exposures for that period were not quantified.
  • The expected number of mesothelioma deaths could not be calculated directly, because general-population mortality rates for this cause were not available. It was estimated from SEER incidence rates, assuming that rates before 1970 were one-half the 1973-1980 rates or lower.
  • 22 deaths had no death certificate.
  • A mortality study is not the most sensitive way to assess the risk of asbestosis.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Asbestos-Containing Material (ACM), Thermal System Insulation (TSI), standardized mortality ratio (SMR), Mesothelioma, Lung Cancer, Laryngeal Cancer.

Related studies

• Long-term follow-up mortality study of petroleum refinery and chemical plant employees — S.P. Tsai, E.L. Gilstrap, et al. (1996)
• Maintenance work and asbestos-related cancers in the refinery and petrochemical sector — M.M. Finkelstein (1999)
• Maintenance work and asbestos-related cancers in the refinery and petrochemical sector — M.M. Finkelstein (1999)
• Update of the Texaco mortality study 1947-93: Part II. Analyses of specific causes of death for white men employed in refining, research, and petrochemicals — B.J. Divine, C.M. Hartman, et al. (1999)
• Asbestos exposure and cancer mortality among petroleum refinery workers: a Poisson regression analysis of updated data — F. Montanaro, M. Ceppi, et al. (2004)
• Mortality rates among employees potentially exposed to chrysotile asbestos at two automotive parts factories — M.M. Finkelstein (1989)

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